As Dense Wavelength Division Multiplex (DWDM) technology evolves rapidly, the transmission rate of WDM system increases quickly to meet ever-growing network data service and voice/image service requirements as well as telecom operators' ever-increasing demand for higher transmission bandwidth; at the same time, the reliability of WDM system becomes a prominent issue. On the basis of enhanced reliability of system modules, implementing a good protection solution will bring significant benefit to system reliability.
Presently, there are two types of WDM system protection solutions: one is Optical Multiplex Segment Protection (OMSP), which is also referred to as optical line protection; the other is OChP; the object of the former is primarily to protect transmission optical fibers; while the latter provides equipment-level protection and it employs the following working principle: whenever the signal transmission in a channel is interrupted or the performance is degraded to a certain degree, the switching device of the system will switch the signals from the channel to a protection channel to transmit; whether to perform the switch is solely determined by the determination device in the receiver according to the quality of received signals and requires no additional detection device.
As DWDM technology evolves by leaps and bounds and the transmission rate increases in doubles, the traffic in each channel becomes increasingly heavier, and the role of transmission channels in the network becomes more significant; as a result, the security and reliability of each channel becomes an inevitable factor in the network, which requires better OChP solutions.
One of the common OChP solutions for traditional WDM systems employs 1+1 or 1:1 scheme (where 1+1 represents cold backup; 1:1 represents hot backup; the difference between them lies in whether the protection channel transfers traffic when the working channel operates normally), i.e., a power distribution device is added at the optical signal input end of each working Optical Transform Unit (OTU), and one of the two signal outputs of the power distribution device is connected to the working OTU, the other signal output is connected to a backup OTU; in this way, in case the working OTU fails, the input signals may be changed to the backup OTU so as to ensure normal operation of the system. A typical 1+1 solution is shown in FIG. 1. And the coupler shown in FIG. 1 may be substituted with a 1×2 optical switch. The solid line portion in FIG. 1 shows routes of working channels, and the dotted line portion shows routes of protection channels. The feature of such a protection solution is that it utilizes a wavelength signal to protect another wavelength signal; therefore the number of working channels is equal to that of protection channels. Though above WDM-based 1+1 OChP solution can solve the problem of channel reliability, it requires higher initial cost of equipment because half of the wavelength resource is wasted.